Typically, a utility obtains electric power from one or more primary power generation sources, such as gas-fired, coal-fired, nuclear and/or hydroelectric power plants, for delivery to customers via a distribution grid. The power supplied by these sources can vary moment-to-moment. Generally, the sources can be regulated to meet the demands of customers while at the same time conforming to the standards for such power, such as nominal voltage and frequency levels.
To supplement the power supplied by these primary sources, it is becoming more common to connect secondary sources of power, such as solar panels and windmills, to the electric distribution grid. Among other advantages, these secondary forms of energy are renewable, in contrast to the primary sources.